19.1.2 Carbon-13 NMR

• What is Carbon-13 NMR spectroscopy used to determine?

  Carbon environments in a molecule
• Unlike Proton NMR, Carbon-13 NMR identifies the carbon skeleton
• Alkane carbons in Carbon-13 NMR have chemical shifts between 0-50 ppm.
• Match the chemical environment with its approximate chemical shift range in Carbon-13 NMR:

  Alkene carbons ↔️ 100-150 ppm

  Carbonyl carbons ↔️ 160-220 ppm

  Aromatic carbons ↔️ 120-170 ppm

  Alkane carbons ↔️ 0-50 ppm
• What does each unique chemical environment in Carbon-13 NMR produce on the spectrum?

  A distinct peak
• The principle behind Carbon-13 NMR is that {}^{13}C</latex> atoms possess a nuclear spin
• Order the following chemical environments by increasing chemical shift (ppm) in Carbon-13 NMR:

  1️⃣ Alkane carbons

  2️⃣ Alkene carbons

  3️⃣ Aromatic carbons
• Each unique carbon environment in a molecule generates a distinct peak in the Carbon-13 NMR spectrum.
• What is the primary purpose of the magnet in Carbon-13 NMR instrumentation?

  Align the nuclei
• Carbon-13 NMR has lower sensitivity compared to Proton NMR
• Which part of a molecule does Carbon-13 NMR specifically examine?

  Carbon skeleton
• Chemical shifts in Carbon-13 NMR are measured in parts per million (ppm).
• What does the number of unique peaks in a Carbon-13 NMR spectrum indicate?

  Number of unique carbon environments
• A molecule with peaks at 30 ppm and 170 ppm has both alkane and carbonyl environments.
• What does the number of unique peaks in a Carbon-13 NMR spectrum indicate?

  Carbon environments
• Benzene has a single peak at 128 ppm due to its six equivalent carbon atoms.
• What chemical shifts indicate the presence of alkane and carbonyl environments in a molecule?

  30 ppm and 170 ppm
• The chemical shift in Carbon-13 NMR is measured in parts per million
• Match the chemical environment with its typical chemical shift range:

  Alkane carbons ↔️ 0-50 ppm

  Alkene carbons ↔️ 100-150 ppm

  Carbonyl carbons ↔️ 160-220 ppm
• Why does benzene show a single peak at 128 ppm in Carbon-13 NMR?

  Six equivalent carbon atoms
• Carbon-13 NMR is used to identify functional groups based on their characteristic chemical shifts
• Match the functional group with its typical chemical shift range:

  Alcohol ↔️ 50-90 ppm

  Ester ↔️ 160-180 ppm

  Ketone ↔️ 200-220 ppm
• A compound with peaks at 30 ppm (alkane) and 175 ppm (ester) indicates the presence of alkane and ester functional groups.
• What atomic mass of carbon is crucial for Carbon-13 NMR?

  13
• Carbon-13 NMR relies on the fact that ${}^{13}C$ atoms have a nuclear spin
• Match the chemical environment with its typical chemical shift range:

  Aromatic carbons ↔️ 120-170 ppm

  Alkene carbons ↔️ 100-150 ppm

  Carbonyl carbons ↔️ 160-220 ppm
• Arrange the key components of Carbon-13 NMR instrumentation in the correct order:

  1️⃣ Magnet

  2️⃣ Radio-frequency transmitter

  3️⃣ Radio-frequency receiver

  4️⃣ Sample holder

  5️⃣ Data acquisition system
• The sensitivity of Carbon-13 NMR is lower compared to Proton NMR
• The number of unique peaks in a Carbon-13 NMR spectrum indicates the number of different carbon environments in the molecule.
• What does the chemical shift in Carbon-13 NMR reflect?

  Electronic environment
• Match the functional group with its typical chemical shift range:

  Alcohol ↔️ 50-90 ppm

  Carboxylic acid ↔️ 170-185 ppm

  Aldehyde ↔️ 190-205 ppm
• To determine the structure of organic compounds using Carbon-13 NMR data, the first step is to analyze the chemical shifts
• In Carbon-13 NMR, each unique carbon environment is identified based on its chemical shift
• Match the chemical environment with its approximate chemical shift range:

  Alkane carbons ↔️ 0-50 ppm

  Alkene carbons ↔️ 100-150 ppm

  Aromatic carbons ↔️ 120-170 ppm

  Carbonyl carbons ↔️ 160-220 ppm
• Peak splitting in Carbon-13 NMR indicates the number of adjacent protons.
• Based on chemical shifts, multiplicities, and the number of distinct carbon environments, one can propose possible structures
• Steps to determine the structure of organic compounds using Carbon-13 NMR data:

  1️⃣ Analyze the chemical shifts

  2️⃣ Determine multiplicity

  3️⃣ Propose possible structures

  4️⃣ Verify with additional data
• In Carbon-13 NMR, the nucleus detected is ${}^{13}C$, whereas in Proton NMR it is ${}^{1}H$.nuclei
• Carbon-13 NMR has lower sensitivity compared to Proton NMR due to the lower natural abundance of ${}^{13}C$.
• While Carbon-13 NMR provides information about the carbon skeleton, Proton NMR focuses on the hydrogen environment